8th HEAD Meeting, 8-11 September, 2004
Session 24 Supernova Remnants and the Interstellar Medium
Poster, Friday, September 10, 2004, 9:00am-10:00pm

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[24.09] High Angular Resolution X-ray and Optical Observations of the Mixed-Morphology Supernova Remnant W28

J. Rho, J.W. Keohane, T.G. Pannuti (SSC/JPL/Caltech), K. Borkowski (NCSU), P.F. Winkler (Middlebury)

We present a high angular resolution Chandra observation and narrow-band optical images of the archetypical mixed-morphology supernova remnant (SNR) W28. The Chandra observation covered the central and southwestern regions of W28: we have augmented this dataset with a mosaicked ROSAT HRI image that samples the entire angular extent of this SNR. Previous ASCA and ROSAT studies of W28 have shown that the plasma conditions differ from other mixed-morphology SNRs in that X-ray spectral variations are seen across W28. The Chandra image reveals that the X-ray emission from the center of this SNR is very clumpy: this central emission is several arcminutes in size and irregular in shape. The spectrum of this central X-ray emission is reasonably fit by an ionization equilibrium thermal model, but two components to this model are required for an adequate fit. Among mixed-morphology SNRs, the presence of a high temperature component is still unique to W28. Also, compared to the hard X-ray emission, the soft X-ray emission from the center of W28 is associated with smaller scale structures. In addition, we find that along the northern boundary of the SNR, the X-ray emission is very soft: this result indicates that the X-ray emitting plasma has significantly cooled at the site of interaction with adjacent clouds. Our mosaicked ROSAT HRI image reveals a surprisingly clumpy structure along the northwestern rim of W28 which resembles a broken shell rather than a smooth shell: such clumpy structure has never been seen before in the shells of SNRs. Finally, our Chandra observation has resolved a hard X-ray source located 20 arcminutes southwest of the center of W28 and on the shell of the SNR: the spectrum of this source is well-fit with a power-law model, suggesting non-thermal emission, which is either pulsar nebula or a background AGN. We will compare the high resolution X-ray image of W28 with our optical images and discuss several mechanisms that may explain the center-filled X-ray emission of this SNR.

The author(s) of this abstract have provided an email address for comments about the abstract: rho@ipac.caltech.edu

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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.